Process for the production of diaryl carbonates

ABSTRACT

A process for catalytic production of diaryl carbonates by oxidative carbonylation of aromatic hydroxy compounds with carbon monoxide and oxygen achieves water removal during reaction by a process comprising the steps of: removing a liquid stream from an oxidative carbonylation reaction mixture in a reaction vessel, subjecting the liquid stream to reduced pressure, and returning at least a portion of dried liquid stream to the reaction vessel. Typical catalyst systems for oxidative carbonylation contain (A) at least one Group 8, 9, or 10 metal having an atomic number of at least 44 or a compound thereof; (B) at least one alkali metal salt; (C) at least one metal co-catalyst; (D) at least one activating organic solvent; and (E) optionally, at least one base.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of copending U.S. application Ser. No. 09/736,885, filed Dec. 14, 2000, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention is related to an improved process for the removal of undesirable water from a chemical reaction for producing products in which water is deleterious to the process and/or products produced therefrom. In particular, the products are carbonate esters, and more particularly diarylcarbonates, prepared by the oxidative carbonylation of aromatic hydroxy compounds, such as by the reaction with carbon monoxide and oxygen in the presence of a catalyst generally containing a metal of group 8, 9, or 10 of the Periodic Table of Elements and a co-catalyst. The process of this invention allows continuous removal of water without depressurization of a reaction vessel.

[0003] Water removal in the oxidative carbonylation of aromatic hydroxy compounds to make diarylcarbonates is a desirable process since it enhances the productivity of the reaction and thus reduces reactor cost per unit mass of product. This is demonstrated by the improvement obtained when molecular sieves are used for water removal in reactions to make diphenyl carbonate (DPC), as described in U.S. Pat. No. 5,399,734 and in co-pending application Ser. No. 09/224,162, filed Dec. 31, 1999.

[0004] U.S. Pat. No. 5,625,091 describes water removal from oxidative carbonylation reaction mixtures under reduced pressure. U.S. Pat. No. 5,498,472 describes water removal from oxidative carbonylation reaction mixtures by excess process gas flow at relatively low pressures. Both of these latter two methods are specific to reaction mixtures containing a specified catalyst type which employs a quaternary salt and a base. An inert stripping agent has also been used for removing water from reaction mixtures for oxidative carbonylation of aromatic hydroxy compounds as described in U.S. Pat. No. 5,917,078.

[0005] The problem to be solved is to develop a reaction process which removes water from an oxidative carbonylation reaction mixture continuously without the requirement of using an entrained gas process or water absorbing agent. In this manner the water content inside the reactor or reactors may be kept below a prescribed value, in a manner which retains the activity of the catalyst system and minimizes the utilities requirements.

BRIEF SUMMARY OF THE INVENTION

[0006] After careful study the present inventors have discovered methods for removing water of reaction in an integrated process for oxidative carbonylation of aromatic hydroxy compounds which avoids the problems of earlier methods. Thus, in one of its embodiments the present invention is a method for preparing a diaryl carbonate which comprises contacting at least one aromatic hydroxy compound with oxygen and carbon monoxide in the presence of an amount effective for carbonylation of a catalyst composition comprising the following and any reaction products thereof:

[0007] (A) at least one Group 8, 9, or 10 metal having an atomic number of at least 44 or a compound thereof;

[0008] (B) at least one alkali metal salt;

[0009] (C) at least one metal co-catalyst;

[0010] (D) at least one activating organic solvent; and

[0011] (E) optionally, at least one base,

[0012] wherein reaction water is removed by a process comprising the steps of:

[0013] (i) removing a liquid stream from an oxidative carbonylation reaction mixture;

[0014] (ii) transferring the liquid stream to a flash vessel wherein the liquid stream to subjected to reduced pressure, whereby a majority of the water is removed;

[0015] (iii) returning at least a portion of a dried liquid stream to a reaction vessel; and

[0016] (iv) optionally adding at least one of make-up aromatic hydroxy compound or other volatile constituent or catalyst component to the reaction vessel or to the dried liquid stream before return to the reaction vessel,

[0017] wherein at least a portion of diaryl carbonate is recovered from a liquid stream either before or after water removal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a flow diagram for a process which removes water.

[0019]FIG. 2 is another flow diagram for a process which removes water.

[0020]FIG. 3 is yet another flow diagram for a process which removes water.

[0021]FIG. 4 is a graph of palladium turn-over number (TON) versus time for a reaction mixture which was depressurized compared to a reaction mixture which was not depressurized using a catalyst system comprising palladium-copper-titanium.

[0022]FIG. 5 is a graph of palladium turn-over number (TON) versus time for a reaction mixture which was depressurized compared to a reaction mixture which was not depressurized using a catalyst system comprising palladium-lead.

DETAILED DESCRIPTION OF THE INVENTION

[0023] For the sake of brevity, the constituents of the catalyst system are defined as “components” irrespective of whether a reaction between said constituents occurs before or during the carbonylation reaction. Thus, the catalyst system may include said components and any reaction products thereof. The terms “reactor” and reaction vessel” are used interchangeably.

[0024] Unless otherwise noted, the term “effective amount”, as used herein, includes that amount of a substance capable of either increasing (directly or indirectly) the yield of the carbonylation product or increasing selectivity toward an aromatic carbonate. Optimum amounts of a given reactant can vary based on reaction conditions and the identity of other constituents, yet can be readily determined in light of the discrete circumstances of a given application.

[0025] Any aromatic hydroxy compound convertible to a carbonate ester may be employed in the present invention. Suitable aromatic hydroxy compounds include monocyclic, polycyclic or fused polycyclic aromatic monohydroxy or polyhydroxy compounds having from 6 to 30, and preferably from 6 to 15 carbon atoms. Illustrative examples include mono- and poly-hydroxy compounds such as phenol, alkylphenols, o-, m- or p-cresol, o-, m- or p-chlorophenol, o-, m- or p-ethylphenol, o-, m- or p-propylphenol, o-, m- or p-methoxyphenol, methyl salicylate, 2,6-dimethylphenol, 2,4-dimethylphenol, 3,4-dimethylphenol, 1-naphthol and 2-naphthol, xylenol, resorcinol, hydroquinone, catechol, cumenol, the various isomers of dihydroxynaphthalene, bis(4-hydroxyphenyl)propane-2,2,α,60 ′-bis(4-hydroxyphenyl)-p-diisopropylbenzene, and bisphenol A. Aromatic mono-hydroxy compounds are particularly preferred with phenol being the most preferred. In the case of substituents on the aromatic hydroxy compound, the substituents are generally 1 or 2 substituents and are preferably from C-1 to C-4 alkyl, C-1 to C-4 alkoxy, fluorine, chlorine or bromine.

[0026] When an aromatic hydroxy compound as a raw material is used as a reaction solvent, then another solvent need not be used. However, the reaction mixture may also optionally contain at least one inert solvent, that is a solvent whose presence does not improve the yield of or selectivity toward the aromatic carbonate. Illustrative inert solvents include, but are not limited to, hexane, heptane, cyclohexane, methylene chloride, or chloroform.

[0027] Other reagents in the method of this invention are oxygen and carbon monoxide, which react with the aromatic hydroxy compound to form the desired diaryl carbonate. The carbon monoxide may be high-purity carbon monoxide or carbon monoxide diluted with another gas which has no negative effects on the reaction, such as nitrogen, noble gases, argon, or carbon dioxide. The oxygen used in the present invention may be high purity oxygen, air, or oxygen diluted with any other gas which has no negative effects on the reaction, such as nitrogen, noble gases, argon, or carbon dioxide. The concentration of inert gas in the reaction gas may amount to 0 to about 60 volume %, preferably 0 to about 20, and more preferably 0 to about 5 volume %. In a particular embodiment the concentration of inert gas is 0 volume % and the reaction gas is free of inert gas.

[0028] The composition of the reaction gases carbon monoxide and oxygen can be varied in broad concentration ranges. Preferably a carbon monoxide:oxygen molar ratio (normalized on carbon monoxide) of 1:(0.001-1.0) is employed, more preferably 1:(0.01-0.5) and still more preferably 1:(0.02-0.3). The reaction gases are not subject to special purity requirements but care must be taken to ensure that no catalyst poisons such as sulfur or compounds thereof are introduced. In the preferred embodiment of the process according to the invention, pure carbon monoxide and pure oxygen are used. In a further preferred embodiment of the process according to the invention, carbon monoxide and oxygen may be added independently of each other. The oxygen addition, in this case, can take place, if desired, together with inert gas. When a reactor cascade is used instead of an individual reactor, the separate oxygen addition preferably proceeds in such a way that the optimal oxygen concentration is ensured in each of the reactors.

[0029] The reaction gas, comprising carbon monoxide, oxygen and, optionally, an inert gas, may be typically introduced at a rate of about 1 to about 100,000 liters (S.T.P.) per liter of reaction solution, preferably about 5 to about 50,000 liters (S.T.P.) per liter of reaction solution and particularly preferably about 10 to about 10,000 liters (S.T.P.) per liter of reaction solution.

[0030] The catalyst employed herein contains at least one Group 8, 9, or 10 metal having an atomic number of at least 44 or a compound thereof, preferably palladium. The palladium material useful as a catalyst (sometimes referred to hereinafter as palladium source) can be in elemental form or it can be employed as a palladium compound. The palladium material can be employed in a form that is substantially soluble in the reaction media or in a form which is substantially insoluble in the reaction media, such as a supported- or polymer-bound palladium species. Thus, useful palladium materials include elemental palladium-containing entities such as palladium black, palladium deposited on carbon, palladium deposited on alumina and palladium deposited on silica; palladium compounds such as palladium chloride, palladium bromide, palladium iodide, palladium sulfate, palladium nitrate, palladium carboxylates, palladium acetate and palladium 2,4-pentanedionate; and palladium-containing complexes involving such compounds as carbon monoxide, amines, nitrites, phosphines and olefins. As used herein, the term “complexes” includes coordination or complex compounds containing a central ion or atom. The complexes may be nonionic, cationic, or anionic, depending on the charges carried by the central atom and the coordinated groups. Other common names for these complexes include complex ions (if electrically charged), Werner complexes, and coordination complexes. Preferred in many instances are palladium (II) salts of organic acids, most often C₂₋₆ aliphatic carboxylic acids, and palladium (II) salts of β-diketones. Palladium (II) acetate and palladium (II) 2,4-pentanedionate (also know as palladium (II) acetylacetonate) are generally most preferred. Mixtures of palladium materials are also contemplated.

[0031] The quantity of the at least one Group 8, 9, or 10 metal catalyst is not particularly limited in the process of the present invention. An effective amount of the at least one Group 8, 9, or 10 metal catalyst, particularly palladium, is, for example, an amount sufficient to provide about 1 gram-atom of metal per 800-1,000,000, more preferably per 4000-1,000,000, still more preferably per 40,000-200,000, and more preferably per 65,000-100,000 moles of aromatic hydroxy compound fed to the reactor. Aromatic hydroxy compound fed to the reactor includes that aromatic hydroxy compound fed directly to the reactor and that aromatic hydroxy compound recycled to a reactor or added as make-up aromatic hydroxy compound, all of which may include catalyst.

[0032] The catalyst employed herein also contains at least one salt with anion selected from tetrafluoroborates, hexafluorophosphates and halides. In preferred embodiments the salt is an alkali metal salt, preferably an alkali metal halide, and more preferably a bromide such as lithium bromide, sodium bromide, or potassium bromide. Sodium bromide is often most preferred by reason of its particular suitability and relatively low cost.

[0033] Mixtures of the aforementioned salts are also suitable for use in the invention. The at least one salt is typically present in the reaction mixture in an amount of about 1-2000 moles, preferably about 2-1500 moles, and more preferably about 5-1000 moles per gram-atom of Group 8, 9, or 10 metal catalyst.

[0034] There also can be used in combination with the Group 8, 9, or 10 metal catalyst and catalyst system at least one quinone and aromatic diol formed by the reduction of said quinone or a mixture thereof. 1,4-benzoquinone and hydroquinone are preferred. In addition, compounds such as 1,2-quinone and catechol, anthraquinone, 9,10-dihydroxyanthracene, and phenanthrenequinone also can be used. When present, the at least one quinone and aromatic diol formed by the reduction of said quinone or a mixture thereof may be present in an amount of about 10-60, and preferably about 25-40 moles of quinone and/or reduction product thereof per gram-atom of Group 8, 9, or 10 metal catalyst.

[0035] In addition to the at least one Group 8, 9, or 10 metal catalyst having an atomic number of at least 44 there is present in the reaction mixtures of the invention an effective amount of at least one metal co-catalyst (component C) containing a metal different from the at least one Group 8, 9, or 10 metal. Suitable metal co-catalysts include all those known in the art which promote formation of carbonate ester from aromatic hydroxy compound under reactive conditions in the presence of the at least one Group 8, 9, or 10 metal catalyst having an atomic number of at least 44. Metal co-catalysts include elemental metals, metal compounds, and precursors thereof which may form catalytically active metal species under the reaction conditions, it being possible for use to be made of the metal in various degrees of oxidation. Metal co-catalysts may be initially soluble in the reaction mixture or initially insoluble as in supported- or polymer-bound metal co-catalyst species. Alternatively, metal co-catalysts may be initially insoluble in the reaction mixture and form soluble metal co-catalyst species during the course of the reaction. Illustrative metal co-catalysts include lead, copper, titanium, and cerium, either alone or in combination. Preferred metal co-catalysts comprise compounds of lead, particularly when used alone or in combination with at least one of titanium, copper, or cerium.

[0036] The at least one metal co-catalyst can be introduced to the carbonylation reaction in various forms, including salts and complexes, such as tetradentate, pentadentate, hexadentate, or octadentate complexes. Illustrative forms may include oxides, halides, carboxylates (for example of carboxylic acids containing from 2-6 carbon atoms), diketones (including beta-diketones), nitrates, complexes containing carbon monoxide, olefins, amines, phosphines and halides, and the like. Suitable beta-diketones include those known in the art as ligands for the metal co-catalysts of the present invention. Examples include, but are not limited to, acetylacetone, benzoylacetone, dibenzoylmethane, diisobutyrylmethane, 2,2-dimethylheptane-3,5-dione, 2,2,6-trimethylheptane-3,5-dione, dipivaloylmethane, and tetramethylheptanedione. The quantity of ligand is preferably not such that it interferes with the carbonylation reaction itself, with the isolation or purification of the product mixture, or with the recovery and reuse of catalyst components (such as palladium). A metal co-catalyst may be used in its elemental form if sufficient reactive surface area can be provided.

[0037] The at least one metal co-catalyst is included in the carbonylation catalyst system in effective amounts. In this context an “effective amount” is an amount of metal co-catalyst (or combination of metal co-catalysts) that increases the number of moles of aromatic carbonate produced per mole of Group 8, 9, or 10 metal catalyst utilized; increases the number of moles of aromatic carbonate produced per mole of salt utilized; or increases selectivity toward aromatic carbonate production beyond that obtained in the absence of the metal co-catalyst (or combination of metal co-catalysts). Optimum amounts of an metal co-catalyst in a given application will depend on various factors, such as the identity of reactants and reaction conditions.

[0038] One preferred class of metal co-catalysts comprises at least one lead source (sometimes referred to hereinafter as lead compound). A lead compound is preferably soluble in a liquid phase under the reaction conditions. Examples of such lead compounds include, but are not limited to, lead oxides, for example PbO, Pb₃O₄, and PbO₂; lead carboxylates, for example lead (II) acetate and lead (II) propionate; inorganic lead salts such as lead (II) nitrate and lead (II) sulfate; alkoxy and aryloxy lead compounds such as lead (II) methoxide, and lead (II) phenoxide; lead complexes such as lead (II) acetylacetonate and phthalocyanine lead, and organolead compounds (that is lead compounds having at least one lead-carbon bond) such as tetraethyl lead. Of these compounds, lead oxides and lead compounds represented by the formula Pb(OR)₂ wherein R is an aryl group having a carbon number from 6 to 10 are preferred. Mixtures of the aforementioned lead compounds are also contemplated.

[0039] Examples of cerium sources (sometimes referred to hereinafter as cerium compounds) include cerium carboxylates such as cerium acetate, and cerium salts of β-diketones such as cerium (III) 2,4-pentanedionate (cerium (III) acetylacetonate). Mixtures of cerium compounds may also be employed. The preferred cerium compounds are cerium 2,4-pentanedionates.

[0040] Examples of titanium sources (sometimes referred to hereinafter as titanium compounds) comprise inorganic titanium salts such as titanium (IV) bromide, titanium (IV) chloride; titanium alkoxides and aryloxides such as titanium (IV) methoxide, titanium (IV) ethoxide, titanium (IV) isopropoxide, titanium (IV) 2-ethylhexoxide, titanium (IV) butoxide, titanium (IV) 2-ethyl-1,3-hexanediolate, titanium (IV) (triethanolaminato)-isopropoxide and titanium(IV) phenoxide; and titanium salts of β-diketones or β-ketoesters such as titanium (IV) diisopropoxide bis(acetylacetonate), titanium (IV) bis(ethyl acetoacetato) diisopropoxide, titanium (IV) oxide bis(2,4-pentanedionate) (or titanium (IV) oxide acetylacetonate). Mixtures of titanium compounds may also be employed. The preferred titanium compounds are titanium (IV) alkoxides and aryloxides such as titanium (IV) butoxide and titanium (IV) phenoxide; and salts of β-diketones or β-ketoesters such as titanium (IV) oxide acetylacetonate and titanium (IV) bis(ethyl acetoacetato)diisopropoxide.

[0041] Examples of copper sources (sometimes referred to hereinafter as copper compounds) comprise inorganic cupric or cuprous salts or copper complexes. Illustrative examples include, but are not limited to, copper (I) chloride, copper (I) bromide, copper (I) iodide; copper (II) chloride, copper (II) bromide, copper (II) iodide; copper carboxylates such as copper acetate, copper gluconate, and copper (II) 2-ethylhexanoate; copper (II) hydroxide, copper alkoxides and aryloxides; copper nitrate; and copper salts of β-diketones such as copper (II) bis(2,4-pentanedionate) (or copper (II) acetylacetonate). Mixtures of copper compounds may also be employed. The preferred copper compounds are 2,4-pentanedionates. Another preferred class of metal co-catalysts comprises a combination of at least one titanium source and at least one copper source.

[0042] In addition to those illustrated above, one or more additional metal co-catalysts may be used in the carbonylation catalyst system, provided any additional metal co-catalyst does not deactivate (i.e. “poison”) the original metal co-catalyst or cocatalyst combination, such that it loses its effectiveness. A non-exclusive listing of additional metal co-catalysts includes iron, ytterbium, zinc, manganese, europium, bismuth, nickel, cobalt, iridium, rhodium, ruthenium, chromium, and yttrium.

[0043] Typically, the at least one metal co-catalyst component C is present in the amount of about 0.1-200 gram-atoms, preferably about 1-150 gram-atoms, and more preferably about 2-100 gram-atoms of total metals in component C per gram-atom of the Group 8, 9, or 10 metal of component A. Total metals in component C means the combination of all the metals in component C which may comprise one metal or more than one metal. In embodiments wherein the metal co-catalyst comprises at least one copper compound and at least one lead compound, then the mole ratio of copper to lead is about 2-10 moles copper to about 100 moles lead. In other embodiments when palladium, titanium, and copper are included in the reaction, the molar ratio of titanium relative to palladium at the initiation of the reaction is in one embodiment in a range of between about 0.1 and about 150, and the molar ratio of copper relative to palladium is at the initiation of the reaction is in one embodiment in a range of between about 0.1 and about 15. In other embodiments the mole ratio of copper to titanium is about 5-20 moles copper to about 2-30 moles titanium.

[0044] Component D is at least one activating organic solvent. In one embodiment the activating organic solvent is at least one polyether; i.e., at least one compound containing two or more C—O—C linkages. The polyether is preferably free of hydroxy groups to maximize its desired activity and avoid competition with the aromatic hydroxy compound in the carbonylation reaction.

[0045] The polyether preferably contains two or more (O—C—C) units. The polyether may be “aliphatic” or mixed aliphatic-aromatic. As used in the identification of the polyether, the term “aliphatic” refers to the structures of hydrocarbon groups within the molecule, not to the overall structure of the molecule. Thus, “aliphatic polyether” includes heterocyclic polyether molecules containing aliphatic groups within their molecular structure. Suitable aliphatic polyethers include diethylene glycol dialkyl ethers such as diethylene glycol dimethyl ether (hereinafter “diglyme”), triethylene glycol dialkyl ethers such as triethylene glycol dimethyl ether (hereinafter “triglyme”), tetraethylene glycol dialkyl ethers such as tetraethylene glycol dimethyl ether (hereinafter “tetraglyme”), polyethylene glycol dialkyl ethers such as polyethylene glycol dimethyl ether and crown ethers such as 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) and 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane). Illustrative mixed aliphatic-aromatic polyethers are diethylene glycol diphenyl ether and benzo-18-crown-6. In one embodiment of the invention tetraglyme is preferred.

[0046] In alternative embodiments, the activating organic solvent can be a nitrile. Suitable nitrile promoters for the present method include C₂₋₈ aliphatic or C₇₋₁₀ aromatic mono- or dinitriles. Illustrative mononitriles include acetonitrile, propionitrile, and benzonitrile. Illustrative dinitriles include succinonitrile, adiponitrile, and benzodinitrile. Mononitriles are generally preferred; more specifically preferred is acetonitrile.

[0047] In further alternative embodiments, the activating organic solvent can be a carboxylic acid amide. Fully substituted amides (containing no NH groups including the amide nitrogen) are preferred. Aliphatic, aromatic or heterocyclic amides may be used. Illustrative amides are dimethylformamide, dimethylacetamide (hereinafter sometimes “DMA”), dimethylbenzamide and N-methylpyrrolidinone (NMP). Particularly preferred are NMP and DMA.

[0048] The activating organic solvent can also be a sulfone, which may be aliphatic, aromatic or heterocyclic. Illustrative sulfones are dimethyl sulfone, diethyl sulfone, diphenyl sulfone and sulfolane (tetrahydrothiophene-1,1-dioxide). Of these, sulfolane is often preferred.

[0049] It is noted that the function of the activating organic solvent, component D, in the present invention is not that of an inert solvent. Rather, the activating organic solvent is an active catalyst component that improves the yield of or selectivity toward the aromatic carbonate. The role of the activating organic solvent, when present, is believed to be to increase the degree of dissociation and ionization of salt of component B, such as sodium bromide, perhaps by forming a complex with the cationic portion of said component, although the invention is in no way dependent on this or any other theory of operation. The amount of component D employed will be an amount effective to optimize diaryl carbonate formation, in general by increasing the yield of the desired diaryl carbonate as evidenced, for example, by an increase in “turnover number”; i.e., the number of moles of diaryl carbonate formed per gram-atom of the Group 8, 9, or 10 metal catalyst component present. This amount is most often about 1-60% by volume, preferably about 1-25% by volume, more preferably about 2-15% by volume, still more preferably about 4-12% by volume, and yet still more preferably about 6-8% by volume based on the total of aromatic hydroxy compound and component D.

[0050] The amount of activating organic solvent component D may, however, typically depend to some extent on the salt component B and the complexing ability of the organic compound employed. Crown ethers, for example, have a very high complexing tendency with metal cations. For example, 15-crown-5 complexes efficiently with sodium and 18-crown-6 with potassium. Such compounds may be used in amounts as low as an equimolar amount based on salt component B. Other compounds useful as component D, such as straight chain polyethers (e.g., diglyme), may be optimally effective at much higher levels. The preferred proportion of any specific material used as activating organic solvent component D can be determined by simple experimentation.

[0051] At least one base (component E) may optionally be present in the reaction mixture. Any effective bases or mixtures thereof, whether organic or inorganic may be used in the process of the invention. In preferred embodiments a base is used which is capable of generating the conjugate base of an aromatic hydroxy compound and not interfering with the function of any catalyst component. Illustrative examples of inorganic bases include, but are not limited to, alkali metal hydroxides and alkali metal carbonates, alkali metal carboxylates or other salts of weak acids or alkali metal salts of aromatic hydroxy compounds, for example alkali metal phenoxides. Obviously, the hydrates of alkali metal phenoxides can also be used in the process. An example of such a hydrate which may be mentioned is sodium phenoxide trihydrate. In general the use of hydrates and the concomitant addition of water to the reaction mixture may lead, inter alia, to poorer conversion rates and decomposition of carbonates formed. Illustrative examples of organic bases include, but are not limited to, onium hydroxides, onium phenoxides, ammonium hydroxides, ammonium phenoxides, phosphonium hydroxides, phosphonium phenoxides, sulfonium hydroxides, sulfonium phenoxides, guanidinium hydroxides, guanidinium phenoxides, tertiary amines which bear as organic radicals C₆-C₁₀ aryl, C₆-C₁₂ aralkyl and/or C₁-C₂₀-alkyl or represent pyridine bases or hydrogenated pyridine bases; for example dimethylbutylamine, triethylamine, tripropylamine, tributylamine, trioctylamine, benzyldimethylamine, dioctylbenzylamine, dimethylphenethylamine, 1dimethylamino-2-phenylpropane, pyridine, N-methylpiperidine, 1,2,2,6,6-pentamethylpiperidine. The base used is preferably an alkali metal salt of an aromatic hydroxy compound, particularly preferably an alkali metal salt of the aromatic hydroxy compound which is also to be converted to the organic carbonate. These alkali metal salts can be lithium salts, sodium salts, potassium salts, rubidium salts or cesium salts. Lithium phenoxide, sodium phenoxide and potassium phenoxide are preferably used; sodium phenoxide is particularly preferred.

[0052] A base may be added as a pure compound or as a precursor compound, such as addition of an alkali metal-comprising base as a precursor for an alkali metal salt of the aromatic hydroxy compound which is also to be converted to the organic carbonate. Illustrative alkali metal-comprising bases include, but are not limited to, sodium hydroxide, and sodium salts of weak acids such as sodium carboxylates, sodium acetate, and sodium acetylacetonate. A base may be added to the reaction mixture in any convenient form, such as in solid form or as a liquid or a melt, either in neat form or in a solution. In a further embodiment of the invention, the base is added to the reaction mixture as a solution which contains about 0.1 to about 80% by weight, preferably about 0.5 to about 65% by weight, particularly preferably about 1 to about 50% by weight of the base. The solvents which may optionally be used here are both alcohols or phenols, such as the phenol to be reacted, and inert solvents. Examples of solvents which may be mentioned are dimethylacetamide, N-methylpyrrolidinone, dioxane, t-butanol, cumyl alcohol, isoamyl alcohol, tetramethylurea, diethylene glycol, halogenated hydrocarbons (e.g. chlorobenzene or dichlorobenzene) and ethers, such as tetraethylene glycol dimethyl ether. The solvents may be used alone or in any combination with each other.

[0053] A base, if used, is added in an amount independent of the stoichiometry. The ratio of base to Group 8, 9, or 10 metal having an atomic number of at least 44 is preferably chosen in such a way that at least one base is present in an amount in a range of about 0.1 to about 2500, preferably about 5 to about 1500, more preferably about 50 to 1000, and still more preferably about 100 to 400 molar equivalents of base based on component A.

[0054] The oxidative carbonylation reaction can be carried out in a batch reactor, or a semi-continuous, or continuous reactor system comprising one or more reaction vessels. Reaction vessels suitable for use in the process according to the invention with either homogeneous or heterogeneous catalysts include stirrer vessels, autoclaves and bubble columns, it being possible for these to be employed as individual reactors or as a cascade. In a cascade 2 to 15, preferably 2 to 10, and particularly preferably 2 to 5, reactors may be connected in series.

[0055] The method of the invention is preferably conducted in at least one reaction vessel in which the aromatic hydroxy compound, catalyst system, and any other components are charged to a reactor, pressurized under carbon monoxide and oxygen, and heated. The reaction pressure is most often in a range of about 0.1-51 megapascals, preferably about 0.3-25 megapascals, more preferably about 1.0-17 megapascals and still more preferably about 1.1-15 megapascals. Gas is usually supplied in proportions of about 1-50 mole percent oxygen with the balance being carbon monoxide. Additional gases may be present in amounts that do not deleteriously affect the carbonylation reaction. The gases may be introduced separately or as a mixture. Reaction temperatures in the range of about 30-210° C. and preferably about 50-160° C. are typical, with temperatures in the range of about 80-125° C. being more preferred. Agitation of the reaction mixture in at least one reaction vessel is preferably employed to aid the reaction. Agitation may be performed by any known method, including at least one of stirring or gas sparging.

[0056] In order for the reaction to be as rapid as possible, it is preferred to substantially maintain the total gas pressure and partial pressure of carbon monoxide and oxygen until a desired conversion level of aromatic hydroxy compound is achieved, as described, for example, in U.S. Pat. No. 5,399,734, which is incorporated herein by reference.

[0057] The diaryl carbonates produced by this method may be recovered at any convenient point in the process loop and isolated by conventional techniques. It is often preferred to form and thermally crack an adduct of the diaryl carbonate with the hydroxy aromatic compound, as is described in U.S. Pat. Nos. 5,239,106 and 5,312,955, which are incorporated herein by reference.

[0058] Water removal in an integrated process for oxidative carbonylation of aromatic hydroxy compounds may be illustrated with reference to the flow diagrams of FIGS. 1, 2, and 3. In FIG. 1 at least one reaction vessel (1) has contents comprising aromatic hydroxy compound and catalyst system under pressure of carbon monoxide and oxygen. The reactor contents may be agitated by known means; in the embodiment in FIG. 1 agitation is illustrated by stirrer (4). Carbon monoxide, oxygen, and optional other gas may be fed to a reactor (1) through one or more gaseous feed inlets; in the embodiment in FIG. 1 a single gaseous feed inlet (5) is illustrated. Catalyst and liquid (for example, aromatic hydroxy compound) may be fed to a reactor (1) via one or more feed inlets; in the embodiment in FIG. 1 a single feed inlet (6) is illustrated. A liquid stream to be dried may be removed from reaction vessel (1) via an outlet (7) for transfer to a first disengagement vessel (2). The amount of liquid stream withdrawn per hour may amount to about 0.01 to 30 times, preferably about 0.05 to 20 times, and particularly preferably about 0.1 to 10 times, the contents of the reactor.

[0059] Removal of a liquid stream may be performed by any convenient method, preferably by gravity or pump or a combination thereof. As shown in an embodiment in FIG. 1 a liquid stream may be removed from reaction vessel (1) when the liquid level of reaction mixture reaches a level equivalent to the highest level of outlet (7). Thus, in one embodiment as material is continuously pumped into reaction vessel (1) a corresponding flow of material may transfer continuously to disengagement vessel (2) via outlet (7). In alternative embodiments the liquid level in reaction vessel (1) may go temporarily over the highest level of outlet (7) by temporarily closing outlet (7). In yet other alternative embodiments the liquid level in reaction vessel (1) may be temporarily below the highest level of outlet (7) and transfer to disengagement vessel (2) may be performed by pump. The exact mode of operation at a particular time offers beneficial alternatives and may depend on such factors as the degree of conversion of aromatic hydroxy compound to diarylcarbonate under the particular process conditions.

[0060] Disengagement vessel (2) is not agitated. Not agitated means that no deliberate means of agitation is employed other than adventitious agitation, such as that which may occur when a liquid stream is transferred to or from disengagement vessel (2). By maintaining the liquid stream in disengagement vessel (2) without agitation, gases which had been entrained by agitation in reaction vessel (1) may escape from the liquid stream.

[0061] The liquid stream in disengagement vessel (2) may be at a pressure in a range of between about atmospheric pressure and the pressure in reaction vessel (1). In some embodiments the liquid stream in disengagement vessel (2) may be at a pressure which is lower than that in reaction vessel (1). In one embodiment the liquid stream in disengagement vessel (2) is at essentially the same pressure as the reaction mixture in reaction vessel (1). In another embodiment the liquid stream in disengagement vessel (2) is at essentially the same temperature and pressure as the reaction mixture in reaction vessel (1).

[0062] Although the invention is in no way dependent upon mechanism, it is believed that without agitation oxygen dissolved in the liquid steam in disengagement vessel (2) may be consumed through reaction leaving a high concentration of dissolved carbon monoxide. A high concentration of carbon monoxide and also possibly high temperature in the absence of sufficient oxygen may be detrimental to catalyst activity and lifetime depending upon catalyst composition. The catalyst system must be able to withstand the process sequence, particularly the gas disengagement at the reaction temperature and pressure, such that when it is returned to the reactor following removal of water the catalyst activity is maintained or minimally reduced. It has been unexpectedly found that some catalyst packages do not survive this process at high temperature, and the temperature may need to be lowered for these systems prior to removal of water in flash vessel (3) under reduced pressure. In particular it has been discovered that a catalyst system containing lead and a tetraalkylammonium halide does not retain its activity unless the temperature is lowered prior to removal of water in flash vessel (3). Unexpectedly a catalyst system comprising copper and titanium and an alkali metal halide has been found to retain its activity under the same conditions and does not require lowering of temperature or pressure prior to removal of water.

[0063] Outlet gases (13) from reaction vessel (1) and disengagement vessel (2) are recycled using standard methods. Typically outlet gases are cooled to condense and remove water and other condensable compounds before reuse of gases.

[0064] In one embodiment of the water removal process a liquid stream from disengagement vessel (2) is transferred via outlet (8) to at least one flash vessel (3). A flash vessel for evaporation of water may be any type of apparatus known to those skilled in the art for this purpose. For example, a flash vessel may comprise vertical-pipe, horizontal-pipe, slanting-pipe, rotor or thin-layer, centrifugal, worm and falling-film evaporators, tube-bundle evaporators, basket evaporators, evaporators with external return pipe and forced circulation, evaporators with external heating elements and forced circulation and other evaporators known to those skilled in the art. Furthermore, simple distillation and rectifying columns with accompanying heating elements are also suitable; preferably a flash vessel comprises thin-layer and falling-film evaporators and evaporators with forced circulation and heating elements located internally or externally.

[0065] Flash vessel (3) may represent a single flash vessel or more than one flash vessel, each with at least one stage. In one embodiment at least one flash vessel has more than one stage, for example two or three stages. The liquid stream from disengagement vessel (2) can be transferred continuously, semi-continuously (for example, periodically), or in a batch which essentially empties all of disengagement vessel (2). If desired, the temperature of the liquid stream portion removed from disengagement vessel (2) may be lowered from the temperature of the initial reaction mixture by cooling disengagement vessel (2) or through heat exchange during transfer from outlet (8), or both. When the temperature is lowered, it is typically lowered to a temperature in a range between about 50° C. and about 90° C.

[0066] In flash vessel (3) the liquid stream portion is subjected to a reduced pressure in that the pressure is lower than the pressure in reaction vessel (1). Typically the reduced pressure is in the range of about 0.1-500 kilopascals, preferably about 0.7-53 kilopascals, more preferably about 0.7-40 kilopascals, still more preferably about 0.7-13 kilopascals, and yet still more preferably about 2-7 kilopascals, and a temperature in the range of about 50-160° C. for removal of a majority of the water and varying amounts of aromatic hydroxy compound and any other volatile constituents through outlet (9). Because entrained gases have escaped from the liquid stream in disengagement vessel (2), less aromatic hydroxy compound is entrained and lost from flash vessel (3) when the liquid stream from (8) undergoes pressure drop in flash vessel (3). In the present context majority of water means greater than about 50% by weight, preferably about 50-99% by weight, and more preferably about 50-80% by weight of water in the liquid stream initially.

[0067] Generally, the temperature and pressure in flash vessel (3) are such as to keep the liquid stream portion molten without degrading the catalyst. Volatile material exiting flash vessel (3) through outlet (9) may be sent for recovery and recycle of aromatic hydroxy compound and optional other volatile constituents. The removal of water in flash vessel (3) may be performed under essentially isothermal conditions through supplying heat to flash vessel (3), or the removal of water in flash vessel (3) may be performed under essentially adiabatic conditions. In another embodiment the removal of water in flash vessel (3) may be performed at a temperature lower than that of the feed temperature from outlet (8) but higher than that resulting from adiabatic operation by supplying a lower amount of heat to flash vessel (3) than in the isothermal process. In various embodiments the removal of water in flash vessel (3) may be performed in one embodiment at a temperature which is greater than 30° C. higher than the temperature in the reaction vessel (1); and in another embodiment at a temperature which is at least 35° C. higher than the temperature in the reaction vessel (1). In other embodiments the removal of water in flash vessel (3) may be performed in one embodiment at a temperature which is greater than 30° C. lower than the temperature in the reaction vessel (1); and in another embodiment at a temperature which is at least 35° C. lower than the temperature in the reaction vessel (1). In one embodiment dried liquid stream from flash vessel (3) may be withdrawn through outlet (10) and separated into a stream (11) for recovery and isolation of diaryl carbonate and any catalyst constituents, and a stream (12) for recycle of dried reaction mixture to the reaction vessel (1). Optionally, at least one holding vessel, or at least one filtration device for solid removal, or both may be present between flash vessel (10) and reaction vessel (1). The ratio of stream (11) for recovery and stream (12) for recycle to reaction vessel (1) is in a range of about 0.1-30 and preferably in a range of about 0.5-15. Optionally, make-up aromatic hydroxy compound and optional other volatile constituents and make-up catalyst constituents may be added to a reaction vessel (1) or to a liquid stream at some point in the process loop before return to reaction vessel (1), or both. In one embodiment make-up aromatic hydroxy compound and optional other volatile constituents and make-up catalyst constituents are added to a dried liquid stream returning to a reaction vessel.

[0068] In another embodiment of the invention FIG. 2 shows a flow diagram for an embodiment of the process that is essentially identical in equipment and operation to the process described in the flow diagram of FIG. 1, with the exception that a second disengagement vessel (14) is included between a first disengagement vessel (2) and flash vessel (3). The second disengagement vessel (14) is maintained at lower pressure than the first disengagement vessel. In preferred embodiments the second disengagement vessel (14) is maintained at essentially atmospheric pressure, more preferably at slightly above atmospheric pressure, and still more preferably at a pressure in a range of between about 102 and about 345 kilopascals. A liquid stream in second disengagement vessel (14) at atmospheric pressure experiences loss of dissolved gases when a liquid stream experiences the lower pressure in a second disengagement vessel (14) compared to the pressure in first disengagement vessel (2). A liquid stream from second disengagement vessel (14) is sent to flash vessel (3) through an outlet (16) and treated in the same manner as described for the process in FIG. 1. Because dissolved gases have escaped from the liquid stream in second disengagement vessel (14), less aromatic hydroxy compound is entrained and lost from flash vessel (3) when the liquid stream from (16) undergoes pressure drop in flash vessel (3). Another advantage is that less capacity from the vacuum pump attached to the evaporation unit is required, and it is easier to get to low pressures in the evaporation unit.

[0069] Dissolved gases which escape from a liquid stream through outlet (15) from second disengagement vessel (14) are recycled using standard methods. Typically outlet gases are cooled to condense and remove water and other condensable compounds before reuse of gas.

[0070] One of the advantages of the embodiments of the invention illustrated in FIGS. 1 and 2 is that in various embodiments there is no requirement to depressurize the gas in order to separate it from the liquid prior to the flash operation. Thus, gas recompression costs may be minimized. In addition, the water removal process described herein is more economically viable than using molecular sieves for drying reaction mixtures producing products in which water is deleterious to the process and/or products produced therefrom.

[0071] In still another embodiment of the invention FIG. 3 shows a flow diagram for a process that is essentially identical in equipment and operation to the process described in the flow diagram of FIG. 1, with the exception that no disengagement vessel is present between a reaction vessel (1) and a flash vessel (3). In this embodiment a liquid stream to be dried may be removed from a reaction vessel via an outlet (7) for transfer to a flash vessel (3). Removal of liquid stream may be performed by any convenient method, preferably by pressure differentiation or pump, or a combination thereof. As shown in an embodiment in FIG. 3 a liquid stream may be removed from reaction vessel (1) and transferred to flash vessel (3) where it undergoes depressurization and removal of water under the reduced pressure conditions of flash vessel (3) in the same manner as described for the operation of flash vessel (3) in FIG. 1. In one embodiment, following removal of water, a dried liquid stream from flash vessel (3) may be withdrawn through outlet (10) and separated into a stream (11) for recovery and isolation of diaryl carbonate and any catalyst constituents, and a stream (12) for recycle of dried reaction mixture to the reaction vessel (1), again in the same manner as described in the embodiment illustrated in FIG. 1.

[0072] One of the advantages of the embodiments of the invention illustrated in FIG. 3 is that there is no requirement to disengage the gas from the liquid prior to the flash operation. In addition, the water removal process described herein is more economically viable than using molecular sieves for drying reaction mixtures producing products in which water is deleterious to the process and/or products produced therefrom.

[0073] In the various embodiments of the invention the reduction of the pressure of a liquid stream taken from a reaction vessel (1) to the pressure of a flash vessel (3) may be done in either a single stage or in more than one stage. In some embodiments such as may be illustrated in certain embodiments in FIG. 3 the reduction in pressure of a liquid stream is done in a single stage. In other embodiments such as may be illustrated in certain embodiments in FIGS. 1 and 2 the reduction in pressure of a liquid stream may be done in one or more stages. In a particular embodiment the reduction in pressure of a liquid stream may be done in two to five stages between a reaction vessel (1) and a flash vessel (3).

[0074] In a preferred embodiment water removal in the integrated process for oxidative carbonylation of aromatic hydroxy compounds is continuous. When equilibrium is attained in the process, water levels in the at least one reaction vessel are typically at essentially a constant level of about 1000-10,000 ppm, and preferably about 2000-5000 ppm. Water levels in the dried liquid stream portion exiting flash vessel (3) are typically about 50-2000 ppm, and preferably about 250-1000 ppm.

[0075] Diaryl carbonates produced by the method may be recovered and isolated at any convenient point in the process loop. In various embodiments at least a portion of diaryl carbonate is recovered from dried liquid stream. In other embodiments at least a portion of diaryl carbonate is recovered from a liquid stream before drying. In one embodiment at least a portion of diaryl carbonate is recovered from a liquid stream taken directly from a reactor and before drying. In another embodiment at least a portion of diaryl carbonate is recovered from at least a portion of a liquid stream taken directly from a reactor and before drying. In still other embodiments at least a portion of diaryl carbonate may be recovered from streams taken from at least two points in a process loop.

[0076] Embodiments of the invention are illustrated by the following nonlimiting examples.

EXAMPLE 1

[0077] A reaction was run at 100° C. using a catalyst consisting of palladium acetylacetonate (15 ppm), copper (II) acetylacetonate (Cu(acac)₂; 5 equivalents versus Pd), titanium (IV) oxide acetylacetonate (TiO(acac)₂; 15 equivalents versus Pd), sodium bromide (791 equivalents versus Pd), in the presence of reactant phenol and solvent tetraglyme (tetraethylene glycol dimethyl ether, 7% by volume). Gases used were a mixture of carbon monoxide (91 mole %) and oxygen (9 mole %) at about 12.4 megapascals. Molecular sieves (30 grams, type 3A) were placed in a perforated TEFLON basket mounted on the stir shaft just above the impeller. After one hour, the reactor was depressurized, allowed to stir at ambient pressure for 10 minutes, and then re-pressurized at 100° C., and the reaction was continued. The amount of diphenyl carbonate (DPC) product obtained at progressive time points is shown in FIG. 4. Also shown on the same plot is the DPC obtained in a run obtained under the same conditions, but with no interruption of the reaction by depressurization during the progress of the reaction. The data relating to the run in which the reaction was interrupted by depressurization does not include the period when the reactor was depressurized (after one hour, for 10 minutes). FIG. 4 shows that the depressurization did not adversely affect the catalyst.

COMPARATIVE EXAMPLE 1A

[0078] A reaction was run at 100° C. using a catalyst consisting of palladium acetylacetonate (15 ppm), lead (II) oxide (56 equivalents versus Pd), and tetraethyl ammonium bromide (810 equivalents versus Pd), in the presence of reactant phenol. Gases used were a mixture of carbon monoxide (91%) and oxygen (9%) at about 12.4 megapascals. Molecular sieves (30 grams, type 3A) were placed in a perforated TEFLON basket mounted on the stir shaft just above the impeller. After 60 minutes the system was depressurized at the reaction temperature (100° C.) for 10 minutes, and then repressurized. The amount of diphenyl carbonate (DPC) product obtained at progressive time points are shown in FIG. 5. Also shown on the same plot is the DPC obtained from a run under the same conditions, but with no interruption of the reaction by depressurization during the progress of the reaction. The data relating to the run in which the reaction was interrupted by depressurization does not include the period when the reactor was depressurized (after one hour, for 10 minutes). FIG. 5 shows that the depressurization affected the catalyst performance adversely, making this catalyst suitable in a water removal process under conditions where the temperature is lowered before the depressurization is performed.

COMPARATIVE EXAMPLE 1B

[0079] A reaction was run at 100° C. and about 9.3 megapascals using a catalyst consisting of palladium acetylacetonate (25 ppm), lead (II) oxide (56 equivalents versus Pd), tetraethylammonium bromide (600 equivalents versus Pd), in the presence of reactant phenol. Gases used were a mixture of carbon monoxide (91%) and oxygen (9%). Molecular sieves (30 grams, type 3A) were placed in a perforated TEFLON basket mounted on the stir shaft just above the impeller. After 30 minutes the system was cooled to 60° C. and then depressurized, and stirred at ambient pressure for 36 minutes, and then repressurized at 60° C. to the reaction pressure, and then re-heated to the reaction temperature (100° C.). The amounts of diphenyl carbonate (DPC) product obtained at progressive time points are 6.8% by weight DPC at 0.5 hours (prior to depressurization), 11.3% after reattaining reaction temperature after repressurization, and 18.3% and 23.7% after two subsequent 30 minute periods. The significant amount of DPC obtained after the depressurization-repressurization sequence at 60° C. (instead of at the reaction temperature (100° C.) indicates that the catalyst retains its activity after the depressurization at 60° C.

EXAMPLE 2

[0080] A reaction was run at 100° C. and about 10.3 megapascals using 15 ppm palladium as palladium acetylacetonate, 13 equivalents (versus Pd) of copper as Cu(acac)₂, 27 equivalents (versus Pd) of titanium as TiO(acac)₂, 429 equivalents (versus Pd) of sodium bromide, 805 equivalents (versus Pd) of sodium hydroxide, with tetraglyme constituting 7 volume % of the initial reaction mass, and no molecular sieves. The reaction was stopped after 50 minutes by stopping stirring, depressurizing to atmospheric pressure (requiring 1 minute), and then after an additional 1.5 minutes, cooling the reactor to 60° C. The contents were removed and put into a rotary evaporator at about 60° C., where about 10 grams (g) material were evaporated. The contents were removed from the rotary evaporator, and phenol make-up was added to account for the mass removed during the rotary evaporation process, after which the contents were re-introduced into the reactor and the reaction resumed at about 10.3 megapascals and 100° C. for 30 minutes. The reaction was then stopped by stopping stirring, depressurizing to atmospheric pressure (requiring 1 minute), and then after an additional 1.5 minutes, cooling the reactor to 60° C. The contents were put into a rotary evaporator as before, and about 21 grams were evaporated, and phenol make-up was again added to account for the removed mass before resuming the reaction. The reaction was then permitted to run until a total of 2.33 hours of reaction had occurred. The initial total mass of reactants and catalyst (not including gases) was 99.53 grams. After 2.33 hours of reaction, there was 25.2% by weight of DPC as determined by high performance liquid chromatography (HPLC).

EXAMPLE 3

[0081] A reaction was run at about 10.3 megapascals at 100° C. using 14 ppm palladium as palladium acetylacetonate, 20 equivalents (versus Pd) of copper as Cu(acac)₂, 27 equivalents (versus Pd) of titanium as TiO(acac)₂, 423 equivalents (versus Pd) of sodium bromide, 852 equivalents (versus Pd) of base (sodium hydroxide), with tetraglyme constituting 7% by volume of the initial reaction mass, and no molecular sieves. Gases used were a mixture of carbon monoxide (91%) and oxygen (9%). The reaction was stopped after 30 minutes by cooling the reactor to 60° C., and then depressurizing, and the contents were removed and put into a rotary evaporator at about 60° C., where about 32 grams (g) material were evaporated. The contents were removed from the rotary evaporator, and phenol make-up was added to account for the mass removed during the rotary evaporation process, after which the contents were re-introduced into the reactor and the reaction resumed at about 10.3 megapascals and 100° C. for 30 minutes. The reactor was then cooled to 60° C. and depressurized, and the contents were put into a rotary evaporator as before, and about 19 grams were evaporated, and phenol make-up was again added to account for the removed mass before resuming the reaction. The reaction was then permitted to run until a total of 2.05 hours of reaction had occurred.

[0082] The initial total mass of reactants and catalyst (not including gases) was 98.46 grams. After 2.05 hours of reaction, there was 26.1% by weight of DPC as determined by high performance liquid chromatography (HPLC).

COMPARATIVE EXAMPLE 3A

[0083] A reaction was run using 14 ppm palladium as palladium acetylacetonate, 20 equivalents (versus Pd) of copper as Cu(acac)₂, 27 equivalents (versus Pd) of titanium as TiO(acac)₂, 801 equivalents (versus Pd) of sodium bromide, 452 equivalents (versus Pd) of base (sodium hydroxide), with tetraglyme constituting 7% by volume of the initial reaction mass, and 30 g of molecular sieves (type 3A). Gases used were a mixture of carbon monoxide (91%) and oxygen (9%). The reaction was run at about 12.4 megapascals at 100° C. until a total of 2.5 hours of reaction had occurred.

[0084] The initial total mass of reactants and catalyst (not including gases) was 64.52 grams. After 2.5 hours of reaction there was 29.2% by weight of DPC present in the reaction mixture as determined by HPLC.

COMPARATIVE EXAMPLE 3B

[0085] A reaction was run using 14 ppm palladium as palladium acetylacetonate, 20 equivalents (versus Pd) of copper as Cu(acac)₂, 27 equivalents (versus Pd) of titanium as TiO(acac)₂, 424 equivalents (versus Pd) of sodium bromide, 852 equivalents (versus Pd) of base (sodium hydroxide), with tetraglyme constituting 7% by volume of the initial reaction mass, and no molecular sieves. Gases used were a mixture of carbon monoxide (91%) and oxygen (9%). The reaction was run at about 12.4 megapascals at 100° C. until a total of 2.5 hours of reaction had occurred.

[0086] The initial total mass of reactants and catalyst (not including gases) was 99.86 grams. After 1, 1.5, 2, and 2.5 hours of reaction there was 13.0%, 12.8%, 11.6%, and 10.6% by weight of DPC, respectively, as determined by HPLC.

[0087] Comparison of example 3 with comparative example 3B shows the improvement obtained from water removal (example 3) versus not using water removal (comparative example 3B). Comparison of example 3 with comparative example 3A shows that the evaporative method provides comparable improvement in the reaction performance versus the molecular sieve method for water removal.

EXAMPLE 4 AND COMPARATIVE EXAMPLES 4A AND 4B

[0088] Reactions are run similar to examples 3 and comparative examples 3A and 3B except that a lead source is employed as inorganic co-catalyst. Comparison of example 4 with comparative example 4B shows an improvement in DPC yield obtained from water removal (example 4) versus not using water removal (example 4B ). Comparison of example 4 with comparative example 4A shows that the evaporative method provides comparable improvement in DPC yield versus the molecular sieve method for water removal.

EXAMPLE 5 AND COMPARATIVE EXAMPLES 5A AND 5B

[0089] Reactions are run as in examples 1 and comparative examples 1A and 1B except that a combination of lead source and titanium source is employed as inorganic co-catalyst. Comparison of example 5 with comparative example 5B shows an improvement in DPC yield obtained from water removal (example 5) versus not using water removal (example 5B). Comparison of example 5 with comparative example 5A shows that the evaporative method provides comparable improvement in DPC yield versus the molecular sieve method for water removal.

EXAMPLE 6 AND COMPARATIVE EXAMPLES 6A AND 6B

[0090] Reactions are run as in examples 1 and comparative examples 1A and 1B except that a combination of lead source and copper source is employed as inorganic co-catalyst. Comparison of example 6 with comparative example 6B shows an improvement in DPC yield obtained from water removal (example 6) versus not using water removal (example 6B). Comparison of example 6 with comparative example 6A shows that the evaporative method provides comparable improvement in DPC yield versus the molecular sieve method for water removal.

EXAMPLE 7 AND COMPARATIVE EXAMPLES 7A AND 7B

[0091] Reactions are run as in examples 1 and comparative examples 1A and 1B except that a combination of lead source and cerium source is employed as inorganic co-catalyst. Comparison of example 7 with comparative example 7B shows an improvement in DPC yield obtained from water removal (example 7) versus not using water removal (example 7B). Comparison of example 7 with comparative example 7A shows that the evaporative method provides comparable improvement in DPC yield versus the molecular sieve method for water removal.

[0092] While typical embodiments have been set forth for the purpose of illustration, the foregoing descriptions and examples should not be deemed to be a limitation on the scope of the invention. Accordingly, various modifications, adaptations, and alternatives may occur to one skilled in the art without departing from the spirit and scope of the present invention. 

What is claimed is:
 1. A method for preparing a diaryl carbonate which comprises contacting at least one aromatic hydroxy compound with oxygen and carbon monoxide in the presence of an amount effective for carbonylation of a catalyst composition comprising the following and any reaction products thereof: (A) at least one Group 8, 9, or 10 metal having an atomic number of at least 44 or a compound thereof; (B) at least one alkali metal salt; (C) at least one metal co-catalyst; (D) at least one activating organic solvent; and (E) optionally, at least one base, wherein reaction water is removed by a process comprising the steps of: (i) removing a liquid stream from an oxidative carbonylation reaction mixture in a reaction vessel; (ii) transferring the liquid stream to a flash vessel wherein the liquid stream to subjected to reduced pressure, whereby a majority of the water is removed; (iii) returning at least a portion of a dried liquid stream to the reaction vessel; and (iv) optionally adding at least one of make-up aromatic hydroxy compound or other volatile constituent or catalyst component to the reaction vessel or to the dried liquid stream before return to the reaction vessel, wherein at least a portion of diaryl carbonate is recovered from a liquid stream either before or after water removal.
 2. The method according to claim 1 wherein the aromatic hydroxy compound is phenol.
 3. The method according to claim 1 wherein the at least one Group 8, 9, or 10 metal in component A is palladium.
 4. The method according to claim 3 wherein the at least one palladium source is selected from the group consisting of palladium, palladium black, supported palladium, palladium/carbon, palladium/alumina, palladium/silica, inorganic palladium salts, palladium chloride, palladium bromide, palladium iodide, palladium sulfate, palladium nitrate, organic palladium salts, palladium acetate, palladium oxalate, palladium (II) acetylacetonate, palladium complexes, PdCl₂(PhCN)₂, and PdCl₂(PPh₃)₂.
 5. The method according to claim 1 wherein the at least one alkali metal salt of component B is at least one salt selected from the group consisting of halides, chloride, bromide, tetrafluoroborate, and hexafluorophosphate.
 6. The method according to claim 5 wherein component B is at least one chloride or bromide salt.
 7. The method according to claim 6 wherein component B is an alkali metal bromide.
 8. The method according to claim 6 wherein component B is an alkali metal chloride.
 9. The method according to claim 1 wherein the co-catalyst (C) is at least one compound of lead, cerium, copper, or titanium, or mixtures thereof.
 10. The method according to claim 1 wherein the at least one activating organic solvent is selected from the group consisting of polyethers, nitrites, carboxylic acid amides, and sulfones.
 11. The method according to claim 10 wherein the activating organic solvent is at least one member selected from the group consisting of diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, tetraethylene glycol dialkyl ether, polyethylene glycol dialkyl ether, 15-crown-5, 18-crown-6; acetonitrile; N-methylpyrrolidinone, dimethylacetamide; and sulfolane.
 12. The method according to claim 11 wherein the activating organic solvent is tetraethylene glycol dimethyl ether.
 13. The method according to claim 1 wherein component A is present in the amount of about 1 gram-atom of metal per 800-1,000,000 moles of aromatic hydroxy compound; component B is present in the amount of about 1-2,000 moles per gram-atom of the Group 8, 9, or 10 metal of component A; component C is present in the amount of about 0.1-200 gram-atoms of total metals per gram-atom of the Group 8, 9, or 10 metal of component A; and component D is present in an amount of about 1-60% by volume based on the total volume of aromatic hydroxy compound and component D.
 14. The method according to claim 1 wherein at least one base, component E, is present in an amount in a range of about 0.1 to 5000 equivalents based on component A.
 15. The method according to claim 14 wherein the base is at least one alkali metal hydroxide, onium hydroxide, alkali metal phenoxide, onium phenoxide, guanidinium hydroxide or guanidinium phenoxide.
 16. The method according to claim 15 wherein the base is at least one alkali metal hydroxide or alkali metal phenoxide.
 17. The method according to claim 16 wherein the base is at least one of sodium hydroxide or sodium phenoxide.
 18. The method according to claim 1 wherein the proportion of oxygen is about 1-50 mole percent based on total oxygen and carbon monoxide.
 19. The method according to claim 1 wherein the pressure is in a range of about 0.1-51 megapascals and the temperature is in a range of about 50-160° C. in the reaction vessel.
 20. The method according to claim 1 wherein the temperature of the liquid stream taken from the reaction vessel is maintained at about the temperature of the reaction mixture from which the stream was taken before the liquid stream is subjected to reduced pressure.
 21. The method according to claim 20 wherein the temperature is about 50-160° C.
 22. The method according to claim 1 wherein the temperature of the liquid stream taken from the reaction vessel is lowered from the temperature of the reaction mixture from which the stream was taken before the liquid stream is subjected to reduced pressure.
 23. The method according to claim 22 wherein the temperature is about 50-90° C.
 24. The method according to claim 1 wherein the pressure is in a range of about 0.7-53 kilopascals and the temperature is in a range of about 50-160° C. in the flash vessel.
 25. The method according to claim 24 wherein removal of water in the flash vessel is performed under essentially isothermal conditions.
 26. The method according to claim 24 wherein removal of water in the flash vessel is performed under essentially adiabatic conditions.
 27. The method according to claim 24 wherein removal of water in the flash vessel is performed under conditions between those of adiabatic and isothermal.
 28. The method according to claim 24 wherein removal of water in the flash vessel is performed at a temperature which is greater than 30° C. higher than the temperature in the reaction vessel.
 29. The method according to claim 24 wherein removal of water in the flash vessel is performed at a temperature which is greater than 30° C. lower than the temperature in the reaction vessel.
 30. The method according to claim 1 which further comprises the step of transferring a liquid stream from the reaction vessel to a first disengagement vessel before transfer of liquid stream to the flash vessel, wherein the first disengagement vessel is not agitated.
 31. The method according to claim 30 wherein the reaction vessel and the first disengagement vessel are at essentially the same pressure and temperature.
 32. The method according to claim 30 which further comprises the step of transferring the liquid stream from the first disengagement vessel to a second disengagement vessel before transfer of liquid stream to the flash vessel, wherein the second disengagement vessel is at a lower pressure than the first disengagement vessel.
 33. The method according to claim 1 wherein at least a portion of diaryl carbonate is recovered from the dried liquid stream.
 34. The method according to claim 1 wherein at least a portion of diaryl carbonate is recovered from a liquid stream before water removal.
 35. A method for preparing diphenyl carbonate which comprises contacting phenol with oxygen and carbon monoxide in the presence of an amount effective for carbonylation of a catalyst composition comprising the following and any reaction products thereof: (A) at least one palladium source; (B) sodium bromide; (C) a metal co-catalyst selected from the group consisting of lead, cerium, copper, and titanium, and mixtures thereof; (D) at least one activating organic solvent; and (E) optionally, at least one base, wherein reaction water is removed by a process comprising the steps of: (vii) removing a liquid stream from an agitated oxidative carbonylation reaction mixture in a reaction vessel and transferring the stream to a first disengagement vessel which is not agitated; (viii) transferring a liquid stream from the first disengagement vessel to a flash vessel wherein the liquid stream is subjected to reduced pressure, whereby a majority of the water is removed; (ix) returning at least a portion of a dried liquid stream to the reaction vessel; and (x) optionally adding at least one of make-up aromatic hydroxy compound or other volatile constituent or catalyst component to the reaction vessel or to the dried liquid stream before return to the reaction vessel, wherein at least a portion of diaryl carbonate is recovered from a liquid stream either before or after water removal.
 36. The method according to claim 35 wherein the reaction vessel and the first disengagement vessel are at essentially the same pressure and temperature.
 37. The method according to claim 35 wherein the at least one palladium source is selected from the group consisting of palladium, palladium black, supported palladium, palladium/carbon, palladium/alumina, palladium/silica, inorganic palladium salts, palladium chloride, palladium bromide, palladium iodide, palladium sulfate, palladium nitrate, organic palladium salts, palladium acetate, palladium oxalate, palladium (II) acetylacetonate, palladium complexes, PdCl₂(PhCN)₂, and PdCl₂(PPh₃)₂; the copper source is selected from the group consisting of copper alkoxides, copper aryloxides; copper salts of β-diketones, and copper (II) acetylacetonate; the lead source is selected from the group consisting of lead oxides, PbO, Pb₃O₄, PbO₂; lead carboxylates, lead (II) acetate, lead (II) propionate; lead (II) nitrate, lead (II) sulfate; alkoxy lead compounds, lead (II) methoxide, aryloxy lead compounds, lead (II) phenoxide; lead (II) acetylacetonate, phthalocyanine lead, and tetraethyl lead; the titanium source is selected from the group consisting of titanium (IV) oxide acetylacetonate, titanium (IV) methoxide, titanium (IV) ethoxide, titanium (IV) butoxide, and titanium (IV) phenoxide; and the cerium source is selected from the group consisting of cerium acetate, cerium salts of β-diketones, and cerium (III) acetylacetonate, and the activating organic solvent is tetraglyme.
 38. The method according to claim 35 wherein the pressure is in a range of about 0.1-51 megapascals and the temperature is in a range of about 50-160° C. in the reaction vessel.
 39. The method according to claim 35 wherein the temperature of the liquid stream taken from the reaction vessel is maintained at about the temperature of the reaction mixture from which the stream was taken before the liquid stream is subjected to reduced pressure.
 40. The method according to claim 39 wherein the temperature is about 50-160° C.
 41. The method according to claim 35 wherein a base is added
 42. The method according to claim 41 wherein the base is at least one of sodium hydroxide or sodium phenoxide; or quaternary ammonium hydroxide or quaternary ammonium phenoxide.
 43. The method according to claim 41 wherein the temperature of the liquid stream taken from the reaction vessel is lowered from the temperature of the reaction mixture from which the stream was taken before the liquid stream is subjected to reduced pressure.
 44. The method according to claim 43 wherein the temperature is about 50-100° C.
 45. The method according to claim 35 wherein the pressure is in a range of about 0.7-53 kilopascals and the temperature is in a range of about 50-160° C. in the flash vessel.
 46. The method according to claim 45 wherein removal of water in the flash vessel is performed under essentially isothermal conditions.
 47. The method according to claim 45 wherein removal of water in the flash vessel is performed under essentially adiabatic conditions.
 48. The method according to claim 45 wherein removal of water in the flash vessel is performed under conditions between those of adiabatic and isothermal.
 49. The method according to claim 45 wherein removal of water in the flash vessel is performed at a temperature which is greater than 30° C. higher than the temperature in the reaction vessel.
 50. The method according to claim 45 wherein removal of water in the flash vessel is performed at a temperature which is greater than 30° C. lower than the temperature in the reaction vessel.
 51. The method according to claim 35 which further comprises the step of transferring a liquid stream from the first disengagement vessel to a second disengagement vessel before transfer of liquid stream to the flash vessel, wherein the second disengagement vessel is at a pressure in a range of between about 102 and about 345 kilopascals.
 52. The method according to claim 35 wherein at least a portion of diaryl carbonate is recovered from the dried liquid stream.
 53. The method according to claim 35 wherein at least a portion of diaryl carbonate is recovered from a liquid stream before water removal.
 54. A method for preparing a diaryl carbonate which comprises contacting at least one aromatic hydroxy compound with oxygen and carbon monoxide in the presence of an amount effective for carbonylation of a catalyst composition comprising the following and any reaction products thereof: (A) at least one Group 8, 9, or 10 metal having an atomic number of at least 44 or a compound thereof; (B) at least one alkali metal salt; (C) a metal co-catalyst comprising at least one copper source and at least one titanium source; (D) at least one activating organic solvent; and (E) optionally, at least one base, wherein reaction water is removed by a process comprising the steps of: (i) removing a liquid stream from an oxidative carbonylation reaction mixture in a reaction vessel; (ii) transferring the liquid stream to a flash vessel wherein the liquid stream to subjected to reduced pressure, whereby a majority of the water is removed; (iii) returning at least a portion of a dried liquid stream to the reaction vessel; and (iv) optionally adding at least one of make-up aromatic hydroxy compound or other volatile constituent or catalyst component to the reaction vessel or to the dried liquid stream before return to the reaction vessel, wherein at least a portion of diaryl carbonate is recovered from a liquid stream either before or after water removal.
 55. The method according to claim 54 wherein the aromatic hydroxy compound is phenol.
 56. The method according to claim 54 wherein the at least one Group 8, 9, or 10 metal in component A is palladium.
 57. The method according to claim 54 wherein the at least one palladium source is selected from the group consisting of palladium, palladium black, supported palladium, palladium/carbon, palladium/alumina, palladium/silica, inorganic palladium salts, palladium chloride, palladium bromide, palladium iodide, palladium sulfate, palladium nitrate, organic palladium salts, palladium acetate, palladium oxalate, palladium (II) acetylacetonate, palladium complexes, PdCl₂(PhCN)₂, and PdCl₂(PPh₃)₂.
 58. The method according to claim 54 wherein the at least one alkali metal salt of component B is at least one salt selected from the group consisting of halides, chloride, bromide, tetrafluoroborate, and hexafluorophosphate.
 59. The method according to claim 58 wherein component B is at least one chloride or bromide salt.
 60. The method according to claim 59 wherein component B is an alkali metal bromide.
 61. The method according to claim 59 wherein component B is an alkali metal chloride.
 62. The method according to claim 54 wherein component C is a mixture of: at least one titanium source selected from the group consisting of titanium alkoxides, titanium aryloxides, titanium (IV) methoxide, titanium (IV) ethoxide, titanium (IV) isopropoxide, titanium (IV) 2-ethylhexoxide, titanium(IV) butoxide, titanium (IV) 2-ethyl-1,3-hexanediolate, titanium(IV) phenoxide; titanium salts of β-diketones, titanium salts of β-ketoesters, titanium (IV) diisopropoxide bis(acetylacetonate), titanium (IV) bis(ethyl acetoacetato) diisopropoxide, and titanium (IV) oxide acetylacetonate); and at least one copper source selected from the group consisting of copper alkoxides, copper aryloxides; copper salts of β-diketones, and copper (II) acetylacetonate.
 63. The method according to claim 54 wherein the at least one activating organic solvent is selected from the group consisting of polyethers, nitriles, carboxylic acid amides, and sulfones.
 64. The method according to claim 63 wherein the activating organic solvent is at least one member selected from the group consisting of diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, tetraethylene glycol dialkyl ether, polyethylene glycol dialkyl ether, 15-crown-5, 18-crown-6; acetonitrile; N-methylpyrrolidinone, dimethylacetamide; and sulfolane.
 65. The method according to claim 64 wherein the activating organic solvent is tetraethylene glycol dimethyl ether.
 66. The method according to claim 54 wherein component A is present in the amount of about 1 gram-atom of metal per 800-1,000,000 moles of aromatic hydroxy compound; component B is present in the amount of about 1-2,000 moles per gram-atom of the Group 8, 9, or 10 metal of component A; component C is present in the amount of about 0.1-200 gram-atoms of total metals per gram-atom of the Group 8, 9, or 10 metal of component A; and component D is present in an amount of about 1-60% by volume based on the total volume of aromatic hydroxy compound and component D.
 67. The method according to claim 54 wherein at least one base, component E, is present in an amount in a range of about 0.1 to 5000 equivalents based on component A.
 68. The method according to claim 67 wherein the base is at least one alkali metal hydroxide, onium hydroxide, alkali metal phenoxide, onium phenoxide, guanidinium hydroxide or guanidinium phenoxide.
 69. The method according to claim 68 wherein the base is at least one alkali metal hydroxide or alkali metal phenoxide.
 70. The method according to claim 69 wherein the base is at least one of sodium hydroxide or sodium phenoxide.
 71. The method according to claim 54 wherein the proportion of oxygen is about 1-50 mole percent based on total oxygen and carbon monoxide.
 72. The method according to claim 54 wherein the pressure is in a range of about 0.1-51 megapascals and the temperature is in a range of about 50-160° C. in the reaction vessel.
 73. The method according to claim 54 wherein the temperature of the liquid stream taken from the reaction vessel is maintained at about the temperature of the reaction mixture from which the stream was taken before the liquid stream is subjected to reduced pressure.
 74. The method according to claim 73 wherein the temperature is about 50-160° C.
 75. The method according to claim 54 wherein the temperature of the liquid stream taken from the reaction vessel is lowered from the temperature of the reaction mixture from which the stream was taken before the liquid stream is subjected to reduced pressure.
 76. The method according to claim 75 wherein the temperature is about 50-90° C.
 77. The method according to claim 54 wherein the pressure is in a range of about 0.7-53 kilopascals and the temperature is in a range of about 50-160° C. in the flash vessel.
 78. The method according to claim 77 wherein removal of water in the flash vessel is performed under essentially isothermal conditions.
 79. The method according to claim 77 wherein removal of water in the flash vessel is performed under essentially adiabatic conditions.
 80. The method according to claim 77 wherein removal of water in the flash vessel is performed under conditions between those of adiabatic and isothermal.
 81. The method according to claim 77 wherein removal of water in the flash vessel is performed at a temperature which is greater than 30° C. higher than the temperature in the reaction vessel.
 82. The method according to claim 77 wherein removal of water in the flash vessel is performed at a temperature which is greater than 30° C. lower than the temperature in the reaction vessel.
 83. The method according to claim 54 which further comprises the step of transferring a liquid stream from the reaction vessel to a first disengagement vessel before transfer of liquid stream to the flash vessel, wherein the first disengagement vessel is not agitated.
 84. The method according to claim 83 wherein the reaction vessel and the first disengagement vessel are at essentially the same pressure and temperature..
 85. The method according to claim 83 which further comprises the step of transferring a liquid stream from the first disengagement vessel to a second disengagement vessel before transfer of liquid stream to the flash vessel, wherein the second disengagement vessel is at lower pressure than the first disengagement vessel.
 86. The method according to claim 54 wherein at least a portion of diaryl carbonate is recovered from the dried liquid stream.
 87. The method according to claim 54 wherein at least a portion of diaryl carbonate is recovered from a liquid stream before water removal.
 88. A method for preparing diphenyl carbonate which comprises contacting phenol with oxygen and carbon monoxide in the presence of an amount effective for carbonylation of a catalyst composition comprising the following and any reaction products thereof: (A) at least one palladium source; (B) sodium bromide; (C) a metal co-catalyst comprising at least one copper source and at least one titanium source; (D) at least one activating organic solvent; and (E) optionally, at least one base, wherein reaction water is removed by a process comprising the steps of: (vii) removing a liquid stream from an agitated oxidative carbonylation reaction mixture in a reaction vessel and transferring the stream to a first disengagement vessel which is not agitated; (viii) transferring a liquid stream from the first disengagement vessel to a flash vessel wherein the liquid stream is subjected to reduced pressure, whereby a majority of the water is removed; (ix) returning at least a portion of a dried liquid stream to the reaction vessel; and (x) optionally adding at least one of make-up aromatic hydroxy compound or other volatile constituent or catalyst component to the reaction vessel or to the dried liquid stream before return to the reaction vessel, wherein at least a portion of diaryl carbonate is recovered from a liquid stream either before or after water removal.
 89. The method according to claim 88 wherein the reaction vessel and the first disengagement vessel are at essentially the same pressure and temperature.
 90. The method according to claim 88 wherein the at least one palladium source is selected from the group consisting of palladium, palladium black, supported palladium, palladium/carbon, palladium/alumina, palladium/silica, inorganic palladium salts, palladium chloride, palladium bromide, palladium iodide, palladium sulfate, palladium nitrate, organic palladium salts, palladium acetate, palladium oxalate, palladium (II) acetylacetonate, palladium complexes, PdCl₂(PhCN)₂, and PdCl₂(PPh₃)₂; the copper source is selected from the group consisting of copper alkoxides, copper aryloxides; copper salts of β-diketones, and copper (II) acetylacetonate; the titanium source is selected from the group consisting of titanium (IV) oxide acetylacetonate, titanium (IV) methoxide, titanium (IV) ethoxide, titanium (IV) butoxide, titanium (IV) phenoxide; and the activating organic solvent is tetraglyme.
 91. The method according to claim 88 wherein the pressure is in a range of about 0.1-51 megapascals and the temperature is in a range of about 50-160° C. in the reaction vessel.
 92. The method according to claim 88 wherein the temperature of the liquid stream taken from the reaction vessel is maintained at about the temperature of the reaction mixture from which the stream was taken before the liquid stream is subjected to reduced pressure.
 93. The method according to claim 90 wherein the temperature is about 50-160° C.
 94. The method according to claim 88 wherein a base is added
 95. The method according to claim 94 wherein the base is at least one of sodium hydroxide or sodium phenoxide; or quaternary ammonium hydroxide or quaternary ammonium phenoxide.
 96. The method according to claim 94 wherein the temperature of the liquid stream taken from the reaction vessel is lowered from the temperature of the reaction mixture from which the stream was taken before the liquid stream is subjected to reduced pressure.
 97. The method according to claim 96 wherein the temperature is about 50-100° C.
 98. The method according to claim 88 wherein the pressure is in a range of about 0.7-53 kilopascals and the temperature is in a range of about 50-160° C. in the flash vessel.
 99. The method according to claim 98 wherein removal of water in the flash vessel is performed under essentially isothermal conditions.
 100. The method according to claim 98 wherein removal of water in the flash vessel is performed under essentially adiabatic conditions.
 101. The method according to claim 98 wherein removal of water in the flash vessel is performed under conditions between those of adiabatic and isothermal.
 102. The method according to claim 98 wherein removal of water in the flash vessel is performed at a temperature which is greater than 30° C. higher than the temperature in the reaction vessel.
 103. The method according to claim 98 wherein removal of water in the flash vessel is performed at a temperature which is greater than 30° C. lower than the temperature in the reaction vessel.
 104. The method according to claim 88 which further comprises the step of transferring a liquid stream from the first disengagement vessel to a second disengagement vessel before transfer of liquid stream to the flash vessel, wherein the second disengagement vessel is at a pressure in a range of between about 102 and about 345 kilopascals.
 105. The method according to claim 88 wherein at least a portion of diaryl carbonate is recovered from the dried liquid stream.
 106. The method according to claim 88 wherein at least a portion of diaryl carbonate is recovered from a liquid stream before water removal. 